This invention relates to serial printers and, more particularly, to hammer control apparatus for impact serial printers.
Impact serial printers have taken many forms over the decades with the most common and widespread one being the typewriter. In recent years, the seemingly exponentially increasing use of computer-based high speed information processing systems has placed a strong demand on impact serial printers in terms of speed, performance and reliability. Prior art serial printers especially adapted to print computer-based output data have, in the past, relied upon hard-wired control logic to implement the many control functions and operations required. An example of one such printer is disclosed in U.S. application Ser. No. 505,105 filed in the name of Andrew Gabor on Sept. 11, 1974 for HIGH SPEED PRINTER WITH INTERMITTENT PRINT WHEEL AND CARRIAGE MOVEMENT and assigned to the assignee of the present invention.
In accordance with such prior art serial printers, it has been found advantageous to vary the level of impact force dependent upon the particular character element desired to be struck in order to obtain a substantially uniform print density among all character elements of a particular font style. One way this has been accomplished in the past in connection with a "daisy wheel" type of serial printer is disclosed in U.S. Pat. No. 3,858,509 issued on Jan. 7, 1975 and assigned to the assignee of the present invention. Generally speaking, an ASCII code is used to identify a desired character element to be struck and the desired level of force with which such character element is to be struck.
Oftentimes it is desirable to replace the particular print member being employed in order to change the font style of the character elements. It is also oftentimes desired to print multiple record media simultaneously, e.g. by using carbon paper or the like. In either event, i.e. using a different font style or printing multiple copies, it may be necessary to adjust the impact forces for all characters, i.e. the relative levels of force among the characters remain the same, but the overall force on each is decreased or increased, dependent upon the particular font style employed or number of copies desired to be printed. Such adjustment has, in the past, been effected by mechanical means with its inherent disadvantages, e.g. wear, short life cycle, etc.
It would be desirable, therefore, if the manner of adjusting hammer force levels dependent upon font style or the number of copies to be printed could be accomplished in a more reliable and efficient manner.